Lichen

General information on the partners

The mushroom is called the mycobionte. The Alga and or the cyanobactery names the phycobionte or photobionte.

One approximately estimates the number of lichens at 17.000 species. But a hundred new species are described each year.

The mushrooms implied in lichenous symbiosis account for approximately 1/5 of the whole of currently known mushrooms. Only 2% of the phytobiontes are clearly identified because the morphological characters and the sexuées structures are modified considerably by symbiosis. They are often green algas (chlorophytes). On 200 species on the whole, only one species of yellow and red alga exists.

The kind of the mycobionte depends on the lichen, because the mushroom can live only in symbiosis with a phytobionte. This one can on the other hand live without symbiosis.

When the phytobionte is a cyanobactery, it is about a bacterium of unicellular or filamentous form, very often of the kind Nostoc .

When the phytobionte is a green Algue, in many cases, it belongs to the kind Trebouxia . The alga is made of cell S chlorophyllian which bears the name of Gonidie.

To reproduce, the lichen can present:

of the Isidie S, drawn up structures, ramified on the surface of the thallus in small cylinders made up of algae, surrounded by mycelial filaments;
of the Sorédie S, cells of individual algae, surrounded by Hypha S gathered in a soratie in the shape of wart on the thallus.

In 85% of the cases one has a green alga associated with a mushroom.
In 10% of the cases one has an association of a cyanobactery and a mushroom.
In 5% of the cases the 3 partners are associated.

There exists specificity of a narrow or broad association. The majority of the lichens are moderately specific. Same a mycobionte can join various species of phytobionte.

The oldest fossil of lichen dates from the Dévonien (- 400 million years).

Nutrition

The mycobionte receives nutrients resulting from the photosynthesis of the phytobionte. The phytobionte receives a certain number of mineral compounds coming from the mycobionte. Some are fixing atmospheric Azote.

Morphology and structure of the thalli

One distinguishes three types of lichens according to the total aspect of their thallus.

thallus strongly plated with the support, forming a crust: “crustacean lichen”.
thallus forming of small lobes rounded, as of small sheets which deviate a little from the support: “foliaceous lichen”.
thallus forming of the more or less long, rectified or hanging prolongations: “fructiculeux lichen”.

With regard to the relations between the mycobionte and the phytobionte, one distinguishes three cases from figure.

Hyphe of mushroom is propagated between the cells of the nostoc (blue alga, kind Cyanobactérie) and in its mucilage.
Formation of a appressorium: the two partners have their walls in affixing, coupled one with the other with a light modification. The contact narrower and is sophisticated more.
Formation of a haustorium: the phytobionte ends up being included in the wall of the mycobionte. Here the cytological modifications are large.

Resistance to the extreme conditions

The lichens have the capacity to resist very strong desiccations. Certain lichens can live with a water content of 2%. They are also capable of réhydrater. In general the lichens contain much water (100 to 300% compared to the dry matter of the lichen).

The hydrous resistance of the lichens comes especially from the mycobionte which secretes polysaccharides around the hypha thus creating a zone which traps water in colloidal form. Moreover lichens store polyols, which are used as water reserve. The resumption of the metabolism after a dryness is very fast. The lichen finds its metabolic capacities from 5 to 30 minutes after a rehydration.

the lichens can also survive important temperature variations being able to go from -70 to +70 °C.

Distribution of the lichens

Many species are pionnières, able to colonize extreme mediums. They have very slow growths about a few millimetres per annum. For example, the Rhizocarpon geographicum is a lichen which has a growth of some hundredths of millimetres per annum.

The lichens live very a long time. This characteristic in particular makes it possible to date their support by the report/ratio cuts and speed of growth.

8% of the terrestrial ecosystems are dominated by the lichens. For example, they account for 65% of the flora in extreme cases of the Arctic polar desert.

A plant without border, colonizing the polar circle knowing a court be, just as easily that the moderate north of the forest. The sometimes dry wet areas more in the South have their varieties of lichens…

Indicator of pollution

The requirements out of rock salt are limited enough because the lichens are weak consumers. They are nourished starting from the atmosphere (minerals in the form of aqueous solutions in rainwater). The lichens have also the possibility of solubilizing biogenic salts of the substrate while excreting via mushroom of the organic acids.

The lichens are able to accumulate mineral compounds, well beyond the needs for their organization. This accumulation is extracellular and is done by the mycobionte.

favors: reserve elements like phosphorus.
disadvantage: accumulation of toxic elements.

The lichens concentrate in particular heavy metals, which results in their death. A chart of distribution of the lichens indicates consequently the localization of not polluted zones.

Economic interest

The lichens contain a mucilagineuse substance Amylacé E , the Lichénine to which one recognized nutritive and medicamentous properties.

Food

Food of the Reindeer S: Cladonia rangiferina is the exclusive food of the reindeer, without which the zone Arctique would not be livable. (Erratum: this lichen bears its name in the honor of the reindeer, but actually the reindeers do not eat these lichens Ci, according to recent studies…)
In Canada of immense herds of caribou owes him their survival, Durand the long winter months. In tundra or forest moderate of north, it is a food appreciated of the caribou, dash of America (moose) and some other animals on the occasion. Several variety of lichens are edible for the latter, just a choice preferably, often due for some to the choices of pasture, at the seasons.
In Suisse Evernia divaricata was used a long time to nourish the goats in bad season.
In Asia (the Crimea, Iran…), Lecanora esculenta or “Basket of the desert” is usually consumed by the peasants as by the animals. One has even alleged that the Manne of the desert of the Old will of the Bible could correspond to him.
In Japan, where many Algues (Nori, Konbu, Wakame, Hijiki) belongs to the food and the gastronomy, Umbilicaria esculenta is consumed out of soup, Tenpura and salad under the name of イワタケ (岩竹, “mushroom of the rocks”).
Enfin some species are used as emulsifier and thickening in agribusiness industry.

Medicinal

Medicine used species like the lichen of Iceland ( Cetraria islandica ), the pulmonary ( Sticta pulmonacea ), the lichen pyxidé ( Cladonia pyxidata ) formerly famous for cough, and the lichen of the dog ( Peltigera canina . The tree moss of human cranium ( Usnea plicata ) collected on cranium of hung, was paid at ransom price to cure, believed one, the epilepsy.

If this pharmacopeia fell today into the lapse of memory and certain beliefs of old make from now on smile, the modern medical research (in particular in Drug company and Microbiologie) does not dry up any more praises and nourishes therapeutic hopes, which will perhaps make in their turn smile tomorrow. An example:

Of the extracts of Umbilicaria esculenta appeared strongly inhibiting β-glucosidase, the enzymes which hydrolize disaccharides at the moulds and the cells of mammals, as well as the glucoamylase and of the laminarinase.

Industry teinturière

One draws from the lichens of the rather rich dyes of nuances. Beautiful colors of blue, crimson (red purplished) and purple are given by the parella of Auvergne , Ochrolechia (Lecanora) parella , the orchil of the Canaries ( Roccella tinctoria ). Other species are used traditionally, in particular in Scandinavia:

Rocella phycopsis, Rocella fuciformis, Ochrolechia tartarea, Pertusaria dealbescens, Parmelia glabratula sbsp. fuliginosa and Lasallia pustulata .

Other uses

Indicator of pollution
Perfume (essential oils, one collects some up to 9000 tons per annum)

Toxicity of the lichens

One claimed formerly that no lichen was really vénéneux, except for some intestinal disorders caused by the very bitter species. Thereafter, one reported the use of Letharia vulpina and Cetraria pinastri in Scandinavia to poison the wolves. The toxic principle would act by inhibition of breathing involving the mort.

the orchil extracted (see in the chapter above) was prohibited like food dye because of its toxicity.

Since, as for mushrooms, the list of the toxic lichens does not cease lengthening, among which:

Letharia vulpina, Cetraria pinastri, Xanthoparmelia chlorochroa .

Systematic

The classification of Zahlbruckner (1907,1926), in spite of its seniority, keeps a practical value vis-a-vis often incomplete recent classifications. It breaks up the class of the lichens according to the following diagram:

Subclass of the Ascolichenes : spores produced in the asques ones.
1. Series of the Pyrenocarpeae : ascocarpes opening only by one pore: thalli in general crustacean (approximately 17 families)
2. Series of the Gymnocarpeae : ascocarpes more or less largely opened, thalli of all the types.
  1. Under-series of the Graphidineae : asques and paraphyses destroying and forming with the spores, in the ascocarpe, a pulverulent cluster. The thallus is in majority shellfish, or fruticose. There exist 3 families.
  2. Under-series of the Cyclocarpineae : ascocarpes of round form. It is the group most, where all the types of thalli are. There exist 29 families.
Subclass of the Basidiolichenes (or Hymenolichenes ): spores produced on basides. There exist 3 kinds in all with less than 20 species which are tropical.

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